This invention relates to an integrated optical semiconductor device. More particularly, this invention relates to a monolithic device comprising a multiple heterojunction laser diode of a stripe geometry structure and a photodetector on a common semiconductor substrate. The photodetector is for use in monitoring operation of the laser diode.
Recent semiconductor lasers have high performance and long life. Optical fibers have much been improved. As a result, optical fiber communication systems are stadily developed into practical use. This, in turn, has excited researches and development of integrated optical semiconductor devices in order to attain stable and yet inexpensive optical communication systems.
A semiconductor laser diode with an integrated photodetector is disclosed by K. Iga et al in a report in "Electronics Letters," Vol. 16, No. 9 (Apr. 24, 1980), pages 342-343, under the title of "GaInAsP/InP Laser with Monolithically Integrated Monitoring Detector." It has now been found as will later be discussed with reference to one of twelve figures of the accompanying drawing that it is difficult to manufacture such monolithically integrated semiconductor devices and to raise the photoelectric conversion efficiency of the photodetector and the reproducibility of manufacture and operation. It has also been found that such an integrated optical semiconductor device is not stably operable.